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Linear-light and perceptual uniformity
Each pixel value in a greyscale image represents what is loosely called brightness. However, brightness is defined formally as the attribute of a visual sensation according to which an area appears to emit more or less light. This definition is obviously subjective: Brightness can’t be measured, so is an inappropriate metric for image data. Also, according to colour appearance theory, brightness has no top end: Brightness is not relative to anything.
Intensity is radiant power in a particular direction,that is, power per unit solid angle [W·sr−2]; radiance is intensity per unit projected area. These terms disregard wavelength composition, but in colour imaging, wavelength is important! Neither of these ...
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